Cellular communication systems continue to grow in popularity and have become an integral part of both personal and business communications. Cellular telephones allow users to place and receive phone calls most anywhere they travel. Moreover, as available cellular telephone technology has increased, so too has the functionality of cellular devices. For example, many cellular devices now incorporate Personal Digital Assistant (PDA) features such as calendars, address books, task lists, calculators, memo and writing programs, etc. These multi-function devices usually allow users to wirelessly send and receive electronic mail (email) messages and access the internet via a cellular network and/or a wireless local area network (WLAN), for example.
In the earliest cellular devices, the device included a numeric keyboard and small display for operation of the device. As cellular devices packaged more functionality therein, the typical numeric keypad gave way to the alphanumeric keypad, thereby allowing a user to readily enter full linguistic text. Another consequence of the expansion of cellular device functionality is the desire to increase display size and resolution. A typical tradeoff during design of cellular devices is the exchange of space between the display and the keypad. This design tradeoff may be more problematic as users demand smaller and lighter devices that are easier and more convenient to carry.
An approach to this design tradeoff is to include a touchscreen input in the cellular device. In other words, this approach leans the aforementioned design tradeoff greatly in favor of the display by removing the keypad entirely as an input device, thereby providing the user with a larger display. Typically, an input to a touch screen is intended by the user when placing a finger or stylus on the screen causing the touch screen to generate a variety of signals to identify the location of the touch on the touch screen.
Typical user application scenarios may vary widely for cellular devices. They may be handheld or operated by placing on different surfaces that may or may not be conductive or well-grounded electrically. And such factors, like the effects of electrical grounding of the system, complicate the deciphering of the touch inputs. Also, external/unknown sources (e.g. during device charging or power up) of noise may make deciphering touch inputs problematic.